Instead of displaying long list of post archives in your WordPress site you can display them in a AJAX powered accordion widget so that you visitors can easily browse them by clicking the year and then month accordions. Clicking the year and month drops down the sub lists instantly with AJAX, without any page refresh.
Accordion Archive Widget is the new WordPress widget plugin by Pat Hartl, install and activate it. Upon activation the plugin enables a widget you can add to your sidebar or any other widget area.
For displaying widget, visit your admin area Dashboard -> Appearance -> Widgets page and drag ‘Accordion Archives’ widget to a widget area. That’s it, there are no additional options and settings, you may add a widget title then save the widget.